We propose gene expression profiling for the characterization of innate immunity and adaptive immunity pertinent to solid organ transplantation. We also propose interventional trials that will address critical unmet needs;the clinical studies are underpinned by mechanistic studies. Our proposals were stimulated by our single center studies and evolving literature that mRNA profiling of peripheral blood cells, urinary cells, and bronchoalveolar lavage (BAL) cells are diagnostic of allograft status. Our identification of mRNA profiles of intraoperative renal allograft biopsy specimens that predict acute rejection and renal allograft functional outcome has informed our research design. We propose cooperative multi-site kidney-specific and multi-organ studies to determine whether there is common molecular profile characteristic of inflammatory and immune responses, and which can provide a better method to monitor function and apply interventional modalities aimed at improving graft outcome. In renal allograft recipients, we will investigate whether: (a) acute rejection can be predicted by sequential mRNA profiling of urinary cells;(b) preemptive treatment, based on mRNA profiles, prevents acute rejection and preserves GFR, and (c) mRNA profiles can be used to guide immunosuppression management, such as the withdrawal of calcineurin inhibitors in stable recipients. Studies in diverse groups of transplanted organs will center on the molecular profiling of organ specific and nonspecific injury pathways in the donor prior to procurement and in the recipient immediately after transplantation, and their impact on organ function and alloreactivity. More focused studies will be done in the lung and the liver setting. In lung allografts, we will explore: (a) whether mRNA profiling of cells obtained by donor and recipient BAL cells predict adverse outcomes such as intense inflammation and development of impaired graft function, (b) whether a persistent inflammatory signature of BAL cells is followed by an acute rejection signature. In liver allografts, we will explore: (a) whether an early inflammatory response indicated by a unique mRNA profile of proinflammatory genes is correlated with HCV recurrence, and (b) whether a steroid-avoidance protocol downregulates HCV recurrence in grafts expressing intense inflammatory signature. These mechanistic assays will be carried out with the use of kinetic (real) time quantitative PCR assay, and in select instances with the use of nucleic-acid based microarrays, as well as immunohistologic analysis of the site of gene expression, and are expected to yield data that will be applied in routine clinical care of the transplanted population.